Whilst providing a great many benefits to individuals and organisations, the Internet can be a source of both hidden and known dangers. On the one hand, much of the content available on the Internet is of an undesirable nature, whilst on the other web pages can be a source of malware including spyware, trojans, viruses, etc. One mechanism for defending against these problems is to perform a rating on Uniform Resource Locators (URLs) entered into a web browser on a client terminal, and to present the rating information to the user before downloading the associated web page and/or filter access requests in dependence upon the rating results.
US2008/0163380 describes one such approach involving URL ratings. This involves providing a URL Rating Server which maintains a database of known URLs and their ratings. Client terminals request ratings from the Rating Server, for example prior to downloading a web page. In order to reduce waiting times on the client side, a URL cache is built up in the client terminal based both on previously accessed and trusted URLs, and pre-populated URL rating data obtained, for example, based on a user's profile.
Known approaches to providing URL ratings using a client-server approach suffer from the disadvantages that the database of rated URLs must be extremely large, and that it is extremely difficult to maintain a reliable database given the ever-changing nature of the Internet. The massive growth in web 2.0 sites in particular causes a significant problem for conventional URL rating systems given that dubious and dangerous content can be introduced to the Internet and subsequently removed over extremely short time periods. In fact, known approaches are to a large extent ineffective in view of the changing use patterns now seen with the Internet.